It is important that powder coatings maintain an acceptable smooth surface after the application and curing process. This quality of levelling and smoothness is an inherent property of the powder formulation, but application conditions are also a contributory factor. These conditions include applied thickness of the powder, the quality of spraying, the rate of heating and the curing temperature. Sagging and levelling qualities of powder coatings are influenced by a number of factors, such as particle size and distribution, particle coalescence and surface wetting behaviour, surface tension of the powder, variations in melt viscosity and the characteristics of the curing mechanism. A new quantitative method for predicting the sag and flow properties of a powder coating is described in a recent article by researchers at Nuplex Ltd. Using this technique, they have developed a model that allows the sag and levelling properties of powder coatings to be predicted from their reactivity and rheological properties. This model is claimed to have provided greater insight into the development of low temperature cure powder coatings by Nuplex.
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